1. Field of the Invention
The present invention relates to a multilayered substrate for an ink jet print head, an ink jet print head using it, an ink jet printing apparatus and a method of manufacturing the ink jet print head substrate.
2. Description of the Related Art
An ink jet print head, for example, is constructed of a combination of a head substrate and a nozzle member. The head substrate comprises a base substrate and an ink ejection structure formed of various layers on a surface of the base substrate. The ink ejection structure has heater elements (electrothermal transducers) in an electrothermal conversion system and piezoelectric elements in an electromechanical conversion system. Generally, on the surface of such a head substrate a driver circuit for driving the ink ejection structure and a data input unit for supplying print data to the driver circuit are also formed of various layers.
At present, another construction is being proposed in which a ROM (Read Only Memory) is mounted on the head substrate of the ink jet print head to hold various kinds of data that can be read as required. The data held in the ROM may, for example, include an ID (identity) code of the ink jet print head and data on drive characteristics of the ink ejection structure. Japanese Patent Application Laid-open No. 3-126560 (1991), for example, describes an ink jet print head having an EEPROM (Electrically Erasable Programmable ROM) mounted thereon.
In the ink jet print head disclosed in Japanese Patent Application Laid-open No. 3-126560 (1991), however, since the EEPROM is mounted separately from the head substrate, the print head construction becomes complicated, making reductions in size and weight of the print head and the printing apparatus as a whole difficult. Particularly when there is a large volume of print data, the existing large-capacity ROM chip is useful. But when the volume of print data is small, the use of the large-capacity ROM chip is disadvantageous in terms of cost. U.S. Pat. Nos. 5,504,507 and 5,363,134 disclose a construction in which a ROM consisting of a fuse array is formed in the base substrate of the head substrate of the ink jet print head along with layers such as an ink ejection structure. This construction allows the fuse array, that constitutes the ROM, to be formed at the same time that the layers of ink ejection structure are formed in the base substrate during the process of fabricating the head substrate. The fuses in the array are selectively blown so that desired binary data are held in the fuse array according to the states of the fuses. An ink jet print head using such a head substrate does not need to have a ROM chip prepared separate from the head substrate. Thus the structure for holding various data in a manner that allows them to be read out can be simplified, realizing an improved productivity of the print head and its reduced size and weight.
One method of blowing the fuse element involves, for example, evaporating a fuse portion with a laser beam to open its electrical path. This fuse blowing method, however, is not suited for mass production of the print head because it causes a fused material to adhere to the substrate and because of a prohibitive cost of the blowing process. Another method blows the fuse portion by passing a large electric current through it. Because of a smaller amount of fused material adhering to the substrate and a lower cost, this method is suited for the print head mass production. The method of blowing a fuse by applying a large current, however, has a drawback that since a wattage used to blow the fuse (large capacity rated heat loss) is limited by a resistance of the fuse element, the thermal energy generated is small. Thus, to blow the fuse portion reliably to open the electrical path requires special considerations in the construction of the fuse portion.
Further, since in the ink jet print head ink is present over the substrate, there is a risk that, should an excessively large crack be produced by the blowing of the fuse portion, the ink may get through the crack to reach the substrate. Any ink, once it has infiltrated to the blown fuse portion and electrodes formed on the substrate, can corrode them, impairing the reliability of the ink jet print head.